Treatment apparatus control method

ABSTRACT

This invention provides a method of controlling a treatment apparatus including a treatment chamber adjustable to a desired reduced-pressure atmosphere, a mounting table arranged in the treatment chamber to mount an object to be treated, a cooling medium container provided in the mounting table, and a cooling medium supply system for supplying a cooling medium to the cooling medium container and discharging the cooling medium from the cooling medium container. The method includes the steps of treating the object to be treated while decreasing the temperature of the object to be treated by cooling the mounting table by using heat transfer from the cooling medium supplied to the cooling medium container by the cooling medium supply system, and heating the vicinity of a very small gap which traps moisture in a member constituting the treatment apparatus, when the internal temperature of the treatment apparatus is to be raised.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of controlling a treatmentapparatus and, more particularly, to a method of controlling a treatmentapparatus for treating an object to be treated in a low-temperatureatmosphere.

2. Description of the Related Art

In a technique, such as a dry etching technique, in which a plasma isgenerated by using a reactive gas and an object to be treated is treatedwith this plasma, the object to be treated, such as a semiconductorwafer, is etched while it is cooled in a low-temperature atmosphere, inorder to perform etching in a direction perpendicular to the surface ofthe object to be treated and obtain a high selectivity. In this case, alow-temperature treatment technique using a cooling mechanism isemployed. In this mechanism, a cooling medium container is formed in amounting table for mounting an object to be treated, and a coolingmedium is externally supplied to the cooling medium container to coolthe object to be treated by the resultant heat transfer, therebydecreasing the temperature of the reaction surface of the object.

In a treatment apparatus for performing the low-temperature treatment asmentioned above, individual members are constituted not by a singlematerial, such as aluminum, but by several different types of materialsin accordance with the performance required for each member, e.g.,electrical insulating properties, heat insulating properties, strength,and low-temperature resistance. Additionally, depending on the type of atreatment apparatus, different materials must be airtightly joined sothat neither a gas nor a liquid leaks. In this case, several differentjoining techniques are selectively used in accordance with the types ofmaterials to be joined. For example, a friction welding method is usedin airtightly joining an aluminum member to a stainless steel member, anelectron beam welding method is used in airtightly joining a stainlesssteel member to a Kovar member, and a vacuum brazing method is used inairtightly joining a ceramic member to a Kovar member.

None of the above Joining techniques, however, is perfect. Therefore, ifeven a slight gap is present in a connected portion between membersconstituting a treatment apparatus, moisture in the treatment apparatusenters through this gap by, e.g., a capillary phenomenon. Since thetreatment apparatus is exposed to a severe atmosphere, such as anultra-low-temperature atmosphere, during a treatment, the moistureentering the gap in the joint portion freezes during the treatment. Thetreatment apparatus, on the other hand, is heated up to room temperatureafter the treatment, so the ice defrosts into water again. If themoisture repeatedly freezes and defrosts in the gap, the gap is widenedby volume expansion during the freezing. Consequently, the gap mayproduce cracks in the connected portion or in the constituting members,even if the gap is initially very narrow. If cracks are formed in theconnected portion or in the constituting members, a cooling medium, suchas liquid nitrogen, leaks out from that portion (a cold-leak phenomenon)to vary the internal pressure of the treatment apparatus. This degradesnot only the cooling function but also the function of the overalltreatment apparatus. In extreme cases, the treatment apparatus fails oris broken.

Furthermore, many portions of the cooling mechanism provided in thetreatment apparatus are exposed to the outer atmosphere, so it isimpossible to avoid an intake of external heat, i.e., a temperature risecaused by circulation of a cooling medium. This consequently degradesthe cooling function to make a stable low-temperature treatmentimpossible. For this reason, it is necessary to minimize the intake ofexternal heat in the cooling mechanism.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituations and has its object to provide a method of controlling atreatment apparatus, which can stably perform an operation without afailure by minimizing the intake of external heat in a cooling mechanismand preventing occurrence of a cold leak in individual constitutingmembers of the treatment apparatus and in joint portions between thesemembers.

The above object of the present invention is achieved by a method ofcontrolling a treatment apparatus including a treatment chamberadjustable to a desired reduced-pressure atmosphere, a mounting tablearranged in the treatment chamber to mount an object to be treated, acooling medium container provided in the mounting table, and a coolingmedium supply system for supplying a cooling medium to the coolingmedium container and discharging the cooling medium from the coolingmedium container, comprising the steps of treating the object to betreated while decreasing a temperature of the object to be treated bycooling the mounting table by using heat transfer from the coolingmedium supplied to the cooling medium container by the cooling mediumsupply system, and heating the vicinity of a very small gap which trapsmoisture in a member constituting the treatment apparatus, when aninternal temperature of the treatment apparatus is to be raised.

In the treatment apparatus control method of the present invention, whenthe internal temperature of the treatment apparatus after the treatmentis to be returned from a low temperature to room temperature, portionsof members constituting the treatment apparatus where a cold leak mayoccur, i.e., portions from which a cooling medium leaks out, e.g.,portions where members consisting of different materials are joined orportions where moisture is trapped, such as very small gaps orcapillaries, are heated to sufficiently remove moisture adhered to theseportions. Therefore, freezing of moisture does not take place even whenthe low-temperature treatment is again performed in the treatmentapparatus, so formation of cracks in these portions can be prevented.This makes a stable low-temperature treatment possible.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIGS. 1, 4, 10, 16, and 19 are schematic views showing plasma etchingapparatuses for use in the method of the present invention;

FIGS. 2A to 2E are views for explaining a cold leak;

FIG. 3 is a schematic view showing a cooling medium supply pipe line inwhich occurrence of a cold leak is expected;

FIG. 5 is a schematic view showing a cooling medium supply system inFIG. 4;

FIG. 6 is a sectional view showing an example of a joint deviceapplicable to the plasma etching apparatus in FIG. 4;

FIG. 7 is an enlarged sectional view showing a state in which the jointdevice in FIG. 6 is attached to the plasma etching apparatus in FIG. 4;

FIG. 8 is a schematic view showing a subcooler applicable to the plasmaetching apparatus in FIG. 4;

FIG. 9 is a P-V graph showing the function of the subcooler in FIG. 8;

FIGS. 11 to 14 are schematic views each showing a cooling jacket of theplasma etching apparatus in FIG. 10;

FIG. 15 is a view for explaining the temperature distribution of liquidnitrogen in the cooling jacket;

FIGS. 17 and 18 are schematic views each showing a cooling jacket of theplasma etching apparatus in FIG. 16;

FIG. 20 is a schematic view showing the system configuration of theplasma etching apparatus in FIG. 19;

FIG. 21 is a schematic view showing a main part of another example ofthe system configuration of the plasma etching apparatus in FIG. 19; and

FIG. 22 is a schematic view showing a main part of a cooling jacket ofthe plasma etching apparatus in FIG. 19.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments in which a method of controlling a treatment apparatusaccording to the present invention is applied to a plasma etchingapparatus will be described below with reference to the accompanyingdrawings.

(First Embodiment)

FIG. 1 is a schematic view showing a plasma etching apparatus (to bereferred to as an etching apparatus hereinafter) for use in the methodof the present invention. In FIG. 1, reference numeral 10 denotes theetching apparatus. The etching apparatus 10 has a substantiallycylindrical treatment chamber 11 consisting of a conductive material,e.g., aluminum, and having airtightness (against liquids and gases). Atreatment gas inlet port 12 is formed near the top of the treatmentchamber 11, so that a predetermined treatment gas, such as HF, can beintroduced into the treatment chamber 11 from a gas source via a massflow controller (neither is shown). In addition, an exhaust port 13 isformed near the bottom of the treatment chamber 11, so that thetreatment chamber 11 can be evacuated to a desired reduced-pressureatmosphere via an exhausting means, e.g., a vacuum pump (not shown).

In an almost middle of the treatment chamber 11, a substantiallycolumnar mounting table 15 is so housed as to be kept electricallyinsulated from a bottom 14 of the treatment chamber 11. An object to betreated, such as a semiconductor wafer W, can be mounted on the uppersurface of this mounting table 15. The mounting table 15 is constitutedby a substantially columnar susceptor support table 16 consisting of,e.g., aluminum, and a susceptor 17 detachably mounted on the susceptorsupport table 16 by using, e.g., bolts and consisting of, e.g.,aluminum.

In the susceptor support table 16, a cooling medium container, e.g., acooling jacket 18 for flowing and circulating a cooling medium, such asliquid nitrogen, is formed. This cooling Jacket 18 has a cooling mediumsupply pipe line 19 and a cooling medium discharge pipe line 20.Therefore, a cooling medium supplied from a cooling medium source (notshown) can be introduced into the cooling jacket 18 from the coolingmedium supply pipe line 19 through an appropriate piping means, e.g.,vacuum double-insulated piping, circulated as a coldness source in thecooling jacket 18, and discharged outside the etching apparatus 10through the cooling medium discharge pipe line 20.

The susceptor 17 is a disk-like member having a projecting portion atits center, and a fixing means, such as an electrostatic chuck 21, formounting and fixing the semiconductor wafer W (to be referred to as awafer hereinafter)is provided on the mounting surface of the projectingportion. This electrostatic chuck 21 is formed by, e.g., sandwiching aconductive film such as a copper foil or a silver foil, between twopolyimide films. A Coulomb's force is generated between theelectrostatic chuck 21 and the wafer W by applying a high voltage to theconductive film 22 from a DC high-voltage source 23. This makes itpossible to chuck and hold the wafer W to the surface of theelectrostatic chuck 21. On the mounting surface of the susceptor 17, aheat transfer gas supply means 24 is arranged to supply a heat transfermedium, such as helium gas, from a gas source (not shown) to the lowersurface of the wafer W mounted on the mounting surface.

Also, an annular focus ring 25 is arranged on the upper peripheralportion of the susceptor 17 so as to surround the wafer W. This focusring 25 consists of an insulating material which does not attractreactive ions. Therefore, the focus ring 25 causes reactive ions,generated in the treatment chamber 11, to be incident on only the waferW placed inside the chamber, thereby improving the etching efficiency.

An RF power supply 27 is connected to the susceptor 17 via a matchingcapacitor 26. This RF power supply 27 applies RF power oft e.g., 380 kHzto the susceptor 17 which constitutes the lower electrode. Consequently,a reactive plasma is generated between the susceptor 17 and a top wall28 of the treatment chamber 11, which constitutes the upper electrode,and this makes it possible to etch the surface to be treated of thewafer W.

A heater 29 for temperature adjustment is provided between the susceptor17 and the susceptor support table 16. By applying electric power from apower supply 30 to this heater 29 to allow the heater 29 to function asa heat source, it is possible to optimally adjust the quantity ofcoldness that is transferred to the wafer W from the cooling jacket 18provided in the susceptor support table 16. Similarly, a first heatingmeans 31 consisting of a ceramic heater, a silicon heater, and the likeis provided around the cooling jacket 18. By applying electric powerfrom a power supply 32 to this first heating means 31, it is possible toraise the temperature of a predetermined portion A of the cooling jacket18 to a predetermined temperature. This portion A is a portion (to bereferred to as a moisture trap portion hereinafter) where membersconsisting of different materials are joined, a very small gap orcapillary is present, and a cold leak can take place when moisture istrapped in the gap or capillary. Also, a second heating means 33consisting of a ceramic heater, a silicon heater, and the like isprovided at a predetermined position around the cooling medium supplypipe line 19 and the cooling medium discharge pipe line 20. By applyingelectric power from a power supply 34 to this second heating means 33,it is possible to heat a predetermined portion B, i.e., a moisture trapportion of each of the pipe lines 19 and 20 up to a predeterminedtemperature.

Furthermore, a first temperature detecting means 35, such as afluoroptic temperature probe or a thermocouple, for detecting thetemperature of the wafer W is provided near the electrostatic chuck 21.Information of the temperature detected by this first temperaturedetecting means 35 is transmitted to a controller 36, and the controller36 controls, e.g., the output from the heater 29 on the basis of thisinformation. Likewise, a second temperature detecting means 37 fordetecting the temperature of the predetermined portion A of the coolingjacket 18 is provided near the first cooling means 31. Information ofthe temperature detected by the second temperature detecting means 37 isalso transmitted to the controller 36. A third temperature detectingmeans 38 for detecting the temperature of the predetermined portion B ofeach of the pipe lines 19 and 20 is provided near the second heatingmeans 33. Information of the temperature detected by this thirdtemperature detecting means 38 is also transmitted to the controller 36.

In the cooling jacket 18, an upper liquid level detector 39 and a lowerliquid level detector 40 for measuring the liquid level of the coolingmedium in the cooling jacket 18 are arranged. The upper and lower liquidlevel detectors 39 and 40 transmit information of the liquid level ofthe cooling medium to the controller 36, and the controller 36 adjuststhe supply quantity of the cooling medium to be introduced from thecooling medium supply pipe line 19 into the cooling jacket 18. Theplasma etching apparatus 10 for use in the treatment apparatus controlmethod according to the present invention is arranged as describedabove.

In performing a low-temperature treatment by using the etching apparatuswith the above arrangement, a so-called cold leak may occur in a portionwhere members consisting of different materials are joined, e.g., in aportion (A in FIG. 1) of the wall of the cooling jacket 18 or in aportion (B in FIG. 1) of the cooling medium supply pipe line 19 or thecooling medium discharge pipe line 20, i.e., in a so-called moisturetrap portion. The present invention aims at preventing the occurrence ofthis cold leak in the moisture trap portion and thereby ensure afailure-free operation of the treatment apparatus. To assure a betterunderstanding of the present invention, the mechanism of occurrence ofthe cold leak in the moisture trap portion will be briefly describedbelow with reference to FIGS. 2A to 2E.

As shown in FIG. 2A, even if members consisting of the same material,e.g., a member 41 consisting of stainless steel and stainless steel 42are Joined airtightly (against a gas and a liquid) in a joint portion43, a very small gap or capillary 44 is formed in the joint area.

If the Joint portion having this capillary 44 is exposed to a gascontaining moisture at room temperature, as shown in FIG. 2B, and placedin an atmosphere at an ultra-low temperature, as shown in FIG. 2C, themoisture contained in the gas freezes and adheres, as frost, to theouter surface of that portion. Thereafter, when the joint portion isagain returned to room temperature, as shown in FIG. 2D, the frostadhered on the outer surface melts and forms waterdrops on the surface.These waterdrops are sucked into the capillary of the joint portion by aso-called capillary phenomenon and left behind in the capillary. If thejoint portion is cooled to an ultra-low temperature again with themoisture contained in the capillary, the moisture freezes and expands toproduce a stress in a direction in which the joint portion is separated,as shown in FIG. 2E. If this operation is repeated, cracks are formed inthe joint portion and a cooling medium sealed in that portion leaks insome cases. This phenomenon is generally called a cold leak.

The influence that this cold leak has on the etching apparatus if thecold leak takes place in the cooling medium supply pipe line 19 will bedescribed in detail below with reference to FIG. 3. As shown in FIG. 3,the cooling medium supply pipe line 19 has a double-insulated pipingstructure consisting of, e.g., stainless steel. This double-insulatedpiping structure is constituted by an inner pipe 50 and an outer pipe 51which is concentrically arranged outside the inner pipe 50. A coolingmedium supplied from a cooling medium source (not shown) can beintroduced into the cooling jacket 18 from a supply port through apassage 52 inside the inner pipe 50. The thickness of the inner pipe 50is increased toward the outer circumference in a portion 62 inside thebottom 14 of the treatment chamber.

As a joint portion 53 for connecting the cooling medium supply pipe line19 to the bottom 14 of the etching apparatus 10, first and secondauxiliary pipes 54 and 55 are formed between the inner and outer pipes50 and 51 so as to be coaxially fixed to a flange 56 formed at apredetermined portion of the inner pipe 50. The first and secondauxiliary pipes 54 and 55 effectively prevent leakage of the coolingmedium and escape of heat. With this arrangement, a first annular space57 is formed between the inner pipe 50 and the first auxiliary pipe 54,and a second annular space 58 is formed between the first and secondauxiliary pipes 54 and 55. The first space 57 develops toward thecircumference along the outline of the thick-wall portion of the innerpipe 50 in a portion 63 inside the bottom 14 of the treatment chamber,and extends vertically in a portion 64 along the outer circumference ofthe inner pipe 50.

Spacings between the cooling medium flow path 52 and the first space 57and between the flow path 52 and the second space 58 are airtightlysealed by an appropriate sealing member 59 made of, e.g.,polytetrafluoroethylene (Teflon), polychlorotrifluoroethylene (PCTFE),pulverized fuel ash (PFA), or fluoroelastomer (^(R) Kel-f). In addition,the upper end of the second space 58 opens at the portion 63 of thefirst space 57 which develops toward the outer circumference, and thisopening is airtightly sealed by a sealing member 60. Furthermore, theupper end of the first space 57 communicates with the treatment chamber11 at an opening 61. Therefore, when the treatment chamber 11 isevacuated, the first space 57 is also evacuated. This makes it possibleto increase the insulation efficiency for the cooling medium flowingthrough the cooling medium flow path 52.

when an operation of setting the etching apparatus at an ultra-lowtemperature by introducing a cooling medium, e.g., liquid nitrogen at-196° C. to the cooling medium flow path 52 and returning the apparatusto room temperature is repeatedly executed in the above arrangement,cracks are sometimes formed to cause a cold leak in, e.g., the sealedportions 59 and 60, as explained above with reference to FIGS. 2A to 2E.If the cooling medium is introduced to the flow path 52 with the cracksformed, the cooling medium leaks into the second space 58 through thesealed portion 59, into the first space 57 through the sealed portion60, and into the treatment chamber 11 from the opening 61. Consequently,the gasified liquid nitrogen varies the treatment pressure in thetreatment chamber to degrade the function of the etching apparatus,leading to a reduction in the yield and the throughput of products.

The present invention aims at preventing occurrence of the cold leak asmentioned above. For this purpose, the first and second heating means 31and 33 are provided to heat portions where the cold leak is expected totake place, i.e., portions (moisture trap portions) illustrated by theportions A and B in FIG. 1, e.g., portions where members consisting ofdifferent materials are joined. When the etching apparatus is returnedfrom an ultra-low temperature to room temperature, the first and secondheating means 31 and 33 heat these moisture trap portions to evaporatemoisture present in these portions, thereby removing the moisture.Consequently, the moisture is perfectly removed from the moisture trapportions. Therefore, even if the apparatus is again cooled to anultra-low temperature, no cracks are formed in these moisture trapportions by freezing and expansion of moisture because there is noresidual moisture in these portions. This makes it possible toeffectively prevent occurrence of the cold leak resulting from cracks.

In heating the moisture trap portions, the second and third temperaturedetecting means 37 and 38 arranged near the moisture trap portions tomeasure the temperatures of these portions are used to measure thetemperatures of the moisture trap portions, and information of themeasured values is transmitted to the controller 36. The heating isperformed until the measured values reach a preset value, e.g., 120° C.In this case, it is preferable that the heating be continued for acertain period of time, e.g., 15 minutes in order to completely removemoisture from the moisture trap portions.

It is also possible to heat the moisture trap portions by experimentallydetermining the output of the heating means and/or the heating timerequired to remove moisture from these moisture trap portions andoperating the heating means at a predetermined output for apredetermined time on the basis of the experimentally determined values.When this arrangement is employed, the second and third temperaturedetecting means 37 and 38 can be omitted. Consequently, the structure ofthe etching apparatus 10 can be simplified.

In this manner, it is possible to prevent occurrence of the cold leak inthe moisture trap portions by effectively evaporating moisture fromthese moisture trap portions.

An operation of the plasma etching apparatus to which the treatmentapparatus control method according to the present invention is appliedwill be briefly described below.

First, the wafer W stored in a cassette chamber (not shown) istransferred to a load lock chamber (not shown) by a predeterminedtransfer arm. The wafer W is then transferred from the load lock chamberto the treatment chamber 11, in which the pressure is reduced to apredetermined pressure, e.g., about 1×10⁻⁴ to several tens Torr, througha gate valve 45, and is mounted on the mounting surface of the susceptor17 of the mounting table 15 in the treatment chamber 11. Thereafter, thewafer W is chucked and held by the electrostatic chuck 21.

Subsequently, a cooling medium, e.g., liquid nitrogen is supplied from acooling medium supply source (not shown) into the cooling jacket 18through the cooling medium supply pipe line 19, and the surface to betreated of the wafer W is cooled to a desired temperature by thetransfer of coldness from the cooling medium. This temperature isdetected by the first temperature detecting means 35 at any instant, andthe controller 36 operates the heater 29 or the like on the basis of thedetection signal. Consequently, the wafer W is held at the predeterminedtemperature. In returning the etching apparatus, in which thelow-temperature treatment is performed, to room temperature, the firstand second heating means 31 and 33 heat portions where occurrence of acold leak is expected, i.e., moisture trap portions, thereby removingmoisture from these portions. Therefore, even when a treatment isperformed at an ultra-low temperature, no cold leak takes place due tofreezing and expansion of moisture because there is no residualmoisture. This makes it possible to effectively avoid formation ofcracks in the constituting members.

Subsequently, a treatment gas, e.g., HF is supplied from the treatmentgas inlet port 12 into the treatment chamber 11 held in this optimumtreatment environment, and RF power is applied from the RF power supply27 to the susceptor 17 as the lower electrode. Consequently, a plasma ofthe treatment gas is generated in the treatment chamber 11, and thesurface to be treated of the wafer W is etched by this plasma.

After the etching, the residual treatment gas and the reaction productsare well exhausted from the treatment chamber 11. Thereafter, the waferW is transferred to the load lock chamber through the gate valve 45 andto the cassette chamber by the transfer arm. In this fashion, a seriesof treatment processes are completed.

(Second Embodiment)

This embodiment provides a method of controlling a treatment apparatus,which can stably supply a cooling medium to a mounting table, and, ifthe cooling medium leaks from a cooling medium supply system due to acold leak or other cause, can sense the abnormality of the coolingmedium supply system to stop the supply of the cooling medium before thecooling medium affects the function of the treatment apparatus or makesthe apparatus fail.

That is, this embodiment provides a method of controlling a treatmentapparatus including a pressure stabilizing means provided in a coolingmedium supply system to maintain the supply pressure of a cooling mediumto be supplied to a cooling medium container constant, a pressuredetecting means provided downstream of the pressure stabilizing means todetect the supply pressure of the supplied cooling medium, and anarithmetic means for calculating the change rate of the supply pressureof the cooling medium detected by the pressure detecting means, whereinif the pressure value detected by the pressure detecting means exceeds apredetermined value and the change rate of the pressure value calculatedby the arithmetic means also exceeds a predetermined value, the coolingmedium supply system is shut off to stop the supply of the coolingmedium to the cooling medium container.

In the treatment apparatus control method according to this embodiment,the cooling medium supply pressure maintained constant by the pressurestabilizing means is detected by the pressure detecting means, and, ifboth the supply pressure value of the cooling medium detected by thepressure detecting means and the change rate of the pressure valueexceed their respective predetermined values, the supply of the coolingmedium to the cooling medium container of a mounting table isinterrupted. This makes it possible to sense and avoid an event in whicha cold leak of the cooling medium produces an influence on the functionof the treatment apparatus. Consequently, the cooling medium can besupplied at a stable pressure to the cooling medium container of themounting table, so an object to be treated can be cooled accurately. Itis also possible to carry out a stable low-temperature treatment sincethe supply of the cooling medium can be interrupted before a leakagecooling medium flows into a treatment chamber to adversely affect thetreatment pressure.

A system in which the treatment apparatus control method according tothis embodiment is applied to a plasma etching apparatus will bedescribed below with reference to the accompanying drawings. FIG. 4 is aschematic view showing the plasma etching apparatus according to thisembodiment. In FIG. 4, the same reference numerals as in FIG. 1 denotethe same parts, and a detailed description thereof will be omitted.

As shown in FIG. 5, a cooling medium, e.g., liquid nitrogen is suppliedfrom a cooling medium source 111, e.g., tank to a proper piping means114, e.g., vacuum double-insulated piping via a gas-liquid separator 112and a subcooler 113, and introduced into a cooling jacket 18 formed in asusceptor support table 16 from a cooling medium supply pipe line 19.The cooling medium is then circulated in the cooling jacket 18,discharged from a cooling medium discharge pipe line 20, and exhaustedoutside the system via an evaporator 115.

A pipe lead 122 made of a hollow conductor is formed in a susceptor 17through the susceptor support table 16. Through this pipe lead 122, RFpower of, e.g., 380 kHz can be applied to the susceptor 17 as the lowerelectrode from an RF power supply 125 through a noise-cut filter 123 anda matching capacitor 124, thereby generating a plasma in a treatmentchamber 11. In FIG. 4, a top wall 28 of the treatment chamber 11 whichis grounded outside the apparatus serves as the upper electrode.However, it is also possible to use a hollow member having a largenumber of small holes formed in a surface opposing a wafer and capableof uniformly introducing, into the treatment chamber 11, a treatmentgas, e.g., CF₄ supplied from a treatment gas source through a gas supplypipe line and a mass flow controller.

A temperature adjusting heater 29 is arranged between the susceptor 17and the susceptor support table 16. By applying electric power to thisheater 29 from a power supply 130 through a filter 131 to allow theheater 29 to function as a heat source, it is possible to optimallyadjust the quantity of coldness that is transferred to a wafer W fromthe cooling jacket 18 provided in the susceptor support table 16. Inaddition, a first temperature detecting means 35, e.g., a lacustrone ora thermocouple, for detecting the temperature of the wafer W is providednear an electrostatic chuck 21. Information of the temperature detectedby this first temperature detecting means 35 is transmitted to acontroller 36 through a filter 133, and the controller 36 controls,e.g., the output from the heater 29 on the basis of this information.

A conductive film 22 of the electrostatic chuck 21 is electricallyconnected to a DC high-voltage source 119 through a filter circuit 118.By applying a high voltage from the DC high-voltage source 119, aCoulomb's force is generated between the electrostatic chuck 21 and thewafer W, and this makes it possible to attract and hold the wafer W tothe surface of the electrostatic chuck 21. A plasma etching apparatus 10for use in the treatment apparatus control method according to thisembodiment is arranged as described above.

In the etching apparatus 10 with the above arrangement, in supplying acooling medium from an external cooling medium supply system 150 intothe cooling jacket 18 inside a mounting table 15, it is necessary toobtain electrical insulation between the susceptor support table 16 andthe bottom wall of the treatment chamber 11 and between the coolingmedium supply pipe line 19 and the cooling medium discharge pipe line 20and to prevent leakage of coldness into the treatment chamber 11. Forthis purpose, joint devices 151 as disclosed in Japanese PatentApplication No. 4-353046 filed by the same applicant as the applicant ofthis application are inserted between a cooling medium supply port 135and the cooling medium supply pipe line 19 and between a cooling mediumdischarge port 136 and the cooling medium discharge pipe line 20 in thecooling jacket 18.

The structure of these joint devices 151 will be briefly described belowwith reference to FIGS. 6 and 7. Note that the structure of only thejoint device 151 for the cooling medium supply pipe line 19 isillustrated in an enlarged scale in FIGS. 6 and 7, but the joint devicefor the cooling medium discharge pipe line also has an identicalstructure, so a detailed described thereof will be omitted.

As shown in FIG. 6, this joint device 151 consists primarily of acontainer-side coupling unit 152, an electrically insulatingheat-insulating member 153, and a cooling medium passage-side couplingunit 154. The container-side coupling unit 152 has a flow path at itscenter and is so inserted as to communicate with the cooling mediumcontainer. The heat-insulating member 153 consists of a material, e.g.,ceramics such as alumina, having a low thermal conductivity and highelectrical insulating properties. The member 153 has a flow path at itscenter and is connected to the container-side coupling unit 152. Thecooling medium passage-side coupling unit 154 has a flow path at itscenter and is connected to the heat-insulating member 153 and to thecooling medium supply pipe line 19. Note that the flow paths of thesemembers are so designed as to communicate with each other.

The container-side coupling unit 152 has a three-layer structureconstituted by an end portion 155, a ring member 156, and a buffermember 157. The end portion 155 is entirely fixed airtightly to thepartition wall of the cooling jacket 18 so that the upper supply port135 extends inside the cooling jacket 18. The end portion 155 consistsof a conductive material, e.g., aluminum. The ring member 156 isconnected to the end portion 155 by, e.g., a friction welding method andconsists of stainless steel or the like. The buffer member 157 isconnected to the ring member 156 by, e.g., an electron beam weldingmethod and consists of Kovar or the like. The ring-like heat-insulatingmember 153 is connected to this buffer member 157 by, e.g., a vacuumbrazing method, and realizes electrical insulation for radio frequenciesand insulation of heat for liquid nitrogen.

The cooling medium passage-side coupling unit 154 connected to theheat-insulating member 153 has a vacuum double-pipe structure consistingof, e.g., stainless steel. A buffer member 158 consisting of, e.g.,Kovar is connected to the upper end portion of this double-pipestructure by butt welding or the like. The buffer member 158 isconnected to the heat-insulating member 153 by, e.g., the vacuum brazingmethod. Additionally, an auxiliary heat-insulating member 159 consistingof, e.g., Teflon is fitted on the lower peripheral portion of the buffermember 158.

The vacuum double-insulated structure of the cooling medium passage-sidecoupling unit 154 is constituted by an inner pipe 160 consisting of,e.g., stainless steel, and an outer pipe 161 concentrically arrangedoutside the inner pipe 160 with a predetermined distance between themand consisting of, e.g., stainless steel. The upper portion of the outerpipe 161 is connected to a joint member 162 made of, e.g., stainlesssteel. In this joint member 162, an annular space defined between theinner and outer pipes 160 and 161, i.e., a communication path 164 forallowing a vacuum chamber 163 to communicate with the treatment chamber11 is formed. With this structure, when the treatment chamber 11 isevacuated during a treatment, the vacuum chamber 163 can be evacuated atthe same time, and this prevents outward transfer of coldness. A lowerjoint member 165 having a flow path 164 in its central portion andconsisting of stainless steel or the like is provided at the lower endsof the inner and outer pipes 160 and 161. The lower joint member 165connects the cooling medium supply pipe line 19 of the cooling mediumsupply system 150 to the joint device 151 as described below.

A state in which the cooling medium supply pipe line 19 having a vacuumdouble-insulated pipe structure constituted by outer and inner pipes 167and 168 made of, e.g., stainless steel is connected to the coolingjacket 18 of the etching apparatus 10 by the joint device 151 with the.above arrangement will be described below with reference to FIG. 7.

The lower portion of the joint device 151 is received in a recessedthrough auxiliary member 170 fixed by bolts or the like to a step-likethrough hole formed in a bottom 169 of the treatment chamber.Consequently, a ring-like flow path 171 which permits the treatmentchamber 11 and the vacuum chamber 163 to communicate with each other isformed between the inner circumferential surface of the throughauxiliary member 170 and the outer circumferential surface of the jointdevice. Sealing members 173 and 172 are inserted in a portion C wherethe bottom 169 of the treatment chamber is in contact with the jointmember 162 and in a portion D where the through auxiliary member 170 isin contact with the joint member 162, respectively, in order to sealthese portions from the outer atmosphere.

The upper end of the inner pipe 168 of the cooling medium supply pipeline 19 of the cooling medium supply system 150, in which the coolingmedium flows, is joined to the lower end of the flow path 164 of thelower joint member 165, so that the cooling medium can be supplied intothe inner pipe 160 of the joint device 151. An inner auxiliary stainlesssteel pipe 175 is provided at the upper end of the inner pipe 168 of thecooling medium supply system 150 so as to surround the outer pipe 161 ofthe joint device 151 via a flange-like auxiliary member 177. In aportion indicated by symbol E, the upper ends of the inner auxiliarystainless steel pipe 175 and the outer pipe 167 are airtightly connectedby a sealing member 166 to the bottom 169 of the treatment chamber via astainless steel flange 176. In addition, in a portion indicated bysymbol F, the lower end of the inner auxiliary stainless steel pipe 175is airtightly connected to the upper end of the inner pipe 168 of thecooling medium supply pipe line 19 by a ring-like Teflon seal 174provided in the lower portion of the lower joint member 165.

As discussed above, the cooling medium supplied from the cooling mediumsupply system 150 flows from the flow path formed inside the inner pipe168 of the cooling medium supply pipe line 19 to the flow path formedinside the inner pipe 160 of the joint device 151 without any leak. Thecooling medium is then introduced into the cooling jacket 18 through thecooling medium supply port 135 and used as a coldness source for coolingthe reaction surface of the wafer W, as an object to be treated, to adesired temperature. Since the portions C, D, E, and F are airtightlysealed by the sealing members 173,172, 166, and 174, respectively, nocooling medium leaks into a space 178 defined between the outer pipe 161of the cooling jacket 18 and the inner auxiliary stainless steel pipe175.

The cooling medium used in cooling has an ultra-low temperature of -196°C., in the case of liquid nitrogen. In addition, in the joint portionsand the sealed portions of the pipes for supplying the cooling medium,it is unavoidable to use different materials having different expansioncoefficients, e.g., Teflon and stainless steel. Consequently, asdiscussed earlier in the first embodiment, slight clearances aresometimes formed in the sealed portions C to F by a stress or byfreezing of moisture trapped in small gaps while the operation isrepeatedly performed. In these situations, the cooling medium suppliedthrough the inner pipe 168 of the cooling medium supply pipe line 19passes through the seal 174 in the portion F to enter the space 178formed between the outer pipe 161 of the joint device 151 and theauxiliary stainless steel pipe 175, and further passes through the seals166,172, and 173 in the portions E, D, and C, respectively.Consequently, the cooling medium leaks into the treatment chamber 11through a passage 179 and the passage 171 for evacuation in the space163 formed between the inner and outer pipes 160 and 161 of the jointdevice 151. The cooling medium thus leaking into the treatment chamber11 gasifies in the reduced-pressure atmosphere in the treatment chamberto change the internal pressure of the chamber, producing an adverseeffect on the function of the etching apparatus. If the leakage quantityis extremely large, the etching apparatus itself fails or is damaged.

In this embodiment, therefore, a pressure stabilizing means, e.g., asubcooler 113 for maintaining the supply pressure of the cooling mediumconstant is provided in the cooling medium supply system 150, a pressuredetecting means 180 for detecting the supply pressure of the coolingmedium is provided downstream of the subcooler 113, and an arithmeticmeans 181 for calculating the change rate of the supply pressure of thecooling medium detected by the pressure detecting means 180 is alsoprovided, as in FIG. 5. In this arrangement, the embodiment employs acontrol method by which the cooling medium system is shut off to stopthe supply of the cooling medium to the cooling jacket 18 if thepressure value detected by the pressure detecting means 180 exceeds apredetermined value and the change rate of the pressure value calculatedby the arithmetic means 181 also exceeds a predetermined value.

The system configuration to which the control method of this embodimentis applied will be described below with reference to FIG. 5. Asillustrated in FIG. 5, a cooling medium, e.g., liquid nitrogen containedin the rocks (liquid nitrogen cylinder) 111 is supplied from the vacuumdouble-insulated piping 114 to the gas-liquid separator 112 via a firstvalve 182, and separated into a gas phase and a liquid phase by theseparator 112. When the cooling medium, e.g., liquid nitrogen issupplied through the vacuum double-insulated piping 114 in this way, anintake of external heat is prevented, but the prevention is not perfect.Therefore, gasification of the liquid-phase cooling medium isunavoidable to some extent. In addition, a pressure loss in the pipingdecreases the saturated vapor pressure, and this decreases the liquidtemperature. Consequently, the cooling medium being supplied partiallyevaporates.

If the liquid nitrogen supplied through the piping in this state isintroduced into the cooling jacket 18 by opening the valve, the liquidnitrogen is injected in a state in which the gas and liquid phases aremixed. This makes control of the supply very difficult. In thisembodiment, therefore, the subcooler 113 is provided in the coolingmedium supply system 150 at a position as near as possible to theetching apparatus 10, in order to stabilize the cooling medium supplypressure. This will be described below with reference to FIGS. 8 and 9.

As shown in FIG. 8, the subcooler 113 has a structure in which a heatexchange coil 184 constituted by thin hollow tubes arranged in the formof a ladder is housed in a hollow cylindrical Dewar vessel 183 having anupper portion open in the air. The Dewar vessel 183 is filled withliquid nitrogen. Therefore, the cooling medium supplied in the gasphase-liquid phase mixed state from a supply path α is again cooled byheat exchange in the thin tubes of the heat exchange coil 184 anddischarged as a supercooled liquid to a discharge path β. That is, thesubcooler 113 can perform heat exchange between liquid nitrogen at theatmospheric pressure and liquid nitrogen in the piping by cooling aportion of liquid nitrogen to the atmospheric pressure saturatedtemperature (-196° C.), thereby making a supercooled liquid (thesaturated temperature is -196° C. or more because the pressure in thepiping is higher than the atmospheric pressure).

By supercooling the supplied cooling medium by the subcooler 113 in thismanner, it is possible to shift the P-V state of the cooling medium fromthe position a to the position β in a graph shown in FIG. 9. Therefore,evaporation of the cooling medium can be suppressed, and this reduces aflash loss at the use point. Consequently, the cooling medium can beintroduced into the cooling jacket 18 at a stabilized pressure andtherefore can be controlled easily.

As shown in FIG. 5, the cooling medium supercooled by the subcooler 113as described above is introduced into the cooling jacket 18 from thecooling medium supply pipe line 19 via the joint device 151 andcirculated in the cooling jacket 18. The cooling medium is thendischarged through the cooling medium discharge pipe line 20 andexhausted to the outside via the evaporator 115. In this embodiment, thepressure detector 180 monitors the supply pressure of the cooling mediumat any instant and transmits the detected value to the arithmeticcircuit 181. The arithmetic circuit 181 compares the detected value witha preset reference value. At the same time, the pressure detector 180monitors the internal pressure of the treatment chamber 11 and transmitsthe detected value to the arithmetic circuit 181. The arithmetic circuit181 calculates the change rate of the supply pressure value and comparesthe calculated value with a preset reference value.

It is found that, if a so-called cold leak occurs in the joint device151 as mentioned earlier, the supply pressure of the cooling mediumrises, and the rise is very abrupt. In this embodiment, therefore, thisphenomenon is used as a determination criterion for operating a safetymechanism when a cold leak takes place. That is, in this embodiment, theupper limit of an allowable supply pressure and the upper limit of anallowable supply pressure change rate are preset. If both the pressurevalue detected by the pressure detector 180 and the change ratecalculated by the arithmetic circuit 181 exceed their respective upperlimits, an interrupt signal is transmitted to a second valve 184provided upstream of the subcooler 113, thereby temporarily interruptingthe supply of the cooling medium. With this operation, it is possible toprevent an event in which a cold leak produces a serious influence onthe internal treatment pressure of the treatment chamber 11 or causes afailure or breaking of the etching apparatus 10 itself. In thisembodiment, the pressure value detected by the pressure detector 180 andthe pressure change value calculated by the arithmetic circuit 181 areused as determination criteria for interrupting the supply of thecooling medium. However, the internal pressure value of the treatmentchamber 11 detected by the pressure detector 180 can also be used as adetermination criterion for the control.

An operation of the plasma etching apparatus to which the treatmentapparatus control method according to this embodiment is applicable willbe briefly described below.

As in the first embodiment, the wafer W is transferred from a load lockchamber into the treatment chamber 11 via a gate valve, and chucked andheld on the mounting surface of the susceptor 17 of the mounting table15 by the electrostatic chuck 21.

Subsequently, the cooling medium supply system 150 illustrated in FIG. 5supplies a cooling medium, e.g., liquid nitrogen into the cooling jacket18 via the pressure stabilizing device or the subcooler 113. The surfaceto be treated of the wafer W is cooled to a desired temperature bytransfer of coldness from the cooling medium. This temperature isdetected by the first temperature detecting means 35 at any instant, andthe controller 36 operates the heater 29 or the like on the basis of thedetection signal. In this manner, the wafer W is held at thepredetermined temperature.

In this case, if there is a possibility that a cold leak occurs in thejoint device 151 and the resulting leakage cooling medium flows into thetreatment chamber 11 to vary the internal pressure of the chamber, thesecond valve 184 provided in the cooling medium supply system istemporarily closed by using the pressure value detected by the pressuredetecting means 180 and the change rate of the detected pressure value,as the determination references. Consequently, it is possible to preventvariations in the internal pressure of the treatment chamber 11 or afailure or destruction of the treatment apparatus resulting from a coldleak of the supplied cooling medium.

A treatment gas, e.g., HF is supplied into the treatment chamber 11 heldin this optimum treatment environment, and at the same time RF power isapplied from the RF power supply 125 to the susceptor 17 as the lowerelectrode, thereby generating a plasma in the treatment chamber 11.Consequently, a desired etching treatment can be performed on thesurface to be treated of the wafer W. After the etching, the residualtreatment gas and the reaction products are well exhausted from thetreatment chamber 11. Thereafter, the wafer W is transferred to the loadlock chamber via the gate valve and to a cassette chamber by a transferarm. In this fashion, a series of treatment processes are finished. Inthis embodiment, as in the above embodiment, when the etching apparatusin which the low-temperature treatment is performed is returned to roomtemperature, first and second heating means 31 and 32 heat portionswhere occurrence of a cold leak is expected, i.e., moisture trapportions, thereby removing moisture from these portions. Therefore, evenwhen a treatment is performed at an ultra-low temperature, no cold leaktakes place due to freezing and expansion of moisture because there isno residual moisture. This makes it possible to effectively avoidformation of cracks in the constituting members.

(Third embodiment)

In performing the low-temperature treatment as discussed above, if anexcess liquid-phase cooling medium, e.g., excess liquid nitrogen issupplied to a cooling medium container of an etching apparatus, theliquid-phase cooling medium is sometimes gasified by, e.g., boiling andis discharged directly in a liquid phase from a cooling medium dischargepipe line before the cooling medium acts as an efficient coldnesssource; that is, a so-called overflow phenomenon takes place in somecases. To avoid waste of a cooling medium caused by this overflow,feedback control for the cooling medium supply amount is conventionallyperformed by detecting an optimum filling amount of a cooling medium byusing liquid level detectors provided in a cooling medium container. Todetect the cooling medium filling amount, prism-like liquid leveldetectors, for example, are arranged at predetermined positions, e.g.,two positions at which the upper and lower limits of the liquid levelcan be measured. Measurements are performed by sending light to theprism-like liquid level detectors through optical fibers and making useof the difference in reflectance between portions inside and outside thecooling medium.

If, however, a liquid-phase cooling medium gasifies through, e.g.,boiling, a large number of bubbles are formed, and these bubbles rise tothe surface of the cooling medium all at once. This troubles the surfaceof the cooling medium to result in an unstable liquid level and alsomakes it difficult for the liquid level detectors to accurately detectthe position of the liquid level of the cooling medium, since thebubbles adhere to the liquid level detectors (a hunting phenomenon of aliquid nitrogen valve). In addition, as will be described later withreference to FIG. 15, if boiling strongly occurs at the bottom of acooling medium container, an unstable state in which the temperature atthe bottom is higher than that in the upper portion takes place. Aso-called roll-over phenomenon in which this unstable state transits toa stable state abruptly increases evaporation of a liquid-phase coolingmedium, resulting in a troubled surface and an unstable liquid level ofthe cooling medium. Consequently, it becomes difficult for the liquidlevel detectors to accurately measure the position of the liquid levelof the cooling medium.

This embodiment provides a treatment apparatus control method capable ofstabilizing the detection of the liquid level of a cooling medium byusing an anti-bubble means for stabilizing the liquid level of aliquid-phase cooling medium contained in a cooling medium container, andalso capable of preventing the temperature reversal phenomenon in theliquid-phase cooling medium as discussed above by encouraging transferof coldness between the upper and lower layers of the cooling medium.

That is, this embodiment provides a treatment apparatus control methodcharacterized in that a bubble impinging means, e.g., a staggeredplate-like member or punching plate is arranged in a substantiallyhorizontal direction in a cooling medium container, thereby preventingbubbles produced by boiling in a cooling medium filled region of thecooling medium container from directly rising to the surface of thecooling medium. In this embodiment, it is also possible to use a heatexchanging means, such as a metal heat conductor or a metal heat pipe,for encouraging heat exchange between the upper and lower layers of acooling medium filled in the cooling medium container, or a bubblingdevice capable of gas supply.

A system in which the treatment apparatus control method according tothis embodiment is applied to a plasma etching apparatus will bedescribed below with reference to the accompanying drawings. FIG. 10 isa schematic view showing the plasma etching apparatus according to thisembodiment. In FIG. 10, the same reference numerals as in FIG. 1 denotethe same parts, and a detailed description thereof will be omitted.

A cooling jacket 18 for flowing and circulating a cooling medium isprovided in a susceptor support table 17. A cooling medium supply pipeline 211 and a cooling medium discharge pipe line 212 vertically extendupward from the bottom of the cooling jacket 18 and open at a positionhigher than the liquid level of a cooling medium. During a coolingoperation in this cooling medium supply system, a liquid-phase coolingmedium, e.g., liquid nitrogen supplied from a cooling medium source isintroduced into the cooling jacket 18 from the cooling medium supplypipe line 211 through an appropriate piping means, e.g., stainless steelvacuum double-insulated piping 213. The liquid nitrogen introduced isstored in a liquid phase in the cooling jacket 18 to cause heat exchangeby nuclear boiling primarily near the bottom of the jacket.Consequently, the liquid nitrogen rises as bubbles in the liquid phaseand is stored in the upper portion of the cooling jacket 18. Thegas-phase cooling medium stored in the upper portion of the coolingjacket 18 is then exhausted outside an etching apparatus 10 through thecooling medium discharge pipe line 212 and vacuum double-insulatedpiping 214. In the cooling jacket 18, bubble impinging plates 215 arearranged in a substantially horizontal direction, and upper-and-lowerlayer heat exchanging means 216 are arranged in a substantially verticaldirection. These members stabilize the liquid level and prevent theroll-over of the temperature. Details of this arrangement will bedescribed later with reference to FIGS. 11 to 15.

An upper liquid level detector 39 and a lower liquid level detector 40for measuring the liquid level of the cooling medium in the coolingjacket 18 are also arranged in the cooling Jacket 18. The detectors 39and 40 send information about the liquid level of the cooling medium toa controller 36, so the controller 36 can adjust the supply quantity ofthe cooling medium to be introduced from the cooling medium supply pipeline 211 into the cooling jacket 18. As the liquid level detectors 39and 40, it is possible to use, e.g., prism-like optical liquid leveldetectors. Whether the liquid level detectors 39 and 40 are inside oroutside of the cooling medium can be determined on the basis of thedifference in reflectance of light, which is transmitted to thedetectors through, e.g., optical fibers, between portions inside andoutside the cooling medium. The plasma etching apparatus 10 for use inthe treatment apparatus control method according to this embodiment isarranged as discussed above.

Several examples of the structure of the cooling jacket 18 of a mountingtable designed on the basis of this embodiment will be described belowwith reference to FIGS. 11 to 14. In these examples, the same referencenumerals denote parts having the same functions and a detaileddescription thereof will be omitted.

In the first example of this embodiment illustrated in FIG. 11, aplurality of layers of stationary plates 230 as the bubble impingingmeans 215 are arranged in a substantially horizontal direction so as tobe staggered in the cooing jacket 18 of the mounting table 17. Asdiscussed above, heat transfer is done by gasification of a liquid-phasecooling medium caused by nuclear boiling at the bottom of the coolingjacket 18. With this arrangement of the first example, however, a largenumber of bubbles generated impinge on any of the stationary plates 230to weaken their energy in rising to the surface of the cooling medium.Since the bubbles reach the cooling medium surface in this weakenedstate, they are stored in the upper portion of the cooling jacket 18.This prevents the cooling medium surface from being troubled to resultin an unstable liquid level, or avoids a phenomenon in which bubblesadhere to the surface of the liquid level detector 39. Consequently, theliquid level can be stably, accurately detected. Note that punchingplates can also be used as the stationary plates 230, as well as thestaggered plates.

In an arrangement in FIG. 12, metal heat conductors 231 are additionallyarranged in the vertical direction so as to extend through thestationary plates 230 in the first example in FIG. 11. The metal heatconductors 231 encourage heat exchange between the upper and lowerlayers of a liquid-phase cooling medium, avoiding a so-called roll-overphenomenon.

For easy understanding of the examples illustrated in FIGS. 11 to 14,the roll-over phenomenon will be described with reference to FIG. 15.FIG. 15 shows the temperature distribution of liquid nitrogen filled inthe cooling jacket 18, in which a temperature T rises from the left tothe right in the plane of the paper. As indicated by a solid line inFIG. 15, liquid nitrogen is stable when the temperature in its upperlayer is higher than that in its lower layer. In practice, however,since boiling strongly takes place at the bottom of the cooling Jacket18, liquid nitrogen is in many cases in an unstable state in which thetemperature in the lower layer is higher than that in the upper layer,as indicated by a dotted line in FIG. 15. In this case, since the systemin a cooling medium transits from the unstable state to the stablestate, the upper low-temperature layer and the lower high-temperaturelayer are reversed and mixed by some stimulus, and this sometimes causesan instantaneous large-scale boiling. This phenomenon is called aroll-over phenomenon. Consequently, a large number of bubbles areproduced at once to significantly trouble the surface of a coolingmedium, and this makes an accurate liquid level measurement impossible.Additionally, since an abrupt pressure rise takes place, acountermeasure for releasing this abrupt pressure rise is also required.

The metal heat conductors 231 used in the second example in FIG. 12 arefor avoiding the roll-over phenomenon explained above. That is, sinceheat exchange is performed constantly between the upper and lower layersof liquid nitrogen via the metal heat conductors 231, liquid nitrogen ishardly rendered unstable with the above arrangement. This makes itpossible to avoid occurrence of the roll-over.

In the third example in FIG. 13, heat pipes 232 are arranged verticallyat proper intervals in the cooling jacket 18 in order to further enhancethe heat exchange between the upper and lower layers. In this example, aplurality of layers of punching plates 233 having a large number ofholes are also arranged as the bubble impinging means 215 in asubstantially horizontal direction. It is of course necessary to layerthese punching plates 233 such that holes of the adjacent punchingplates 233 do not overlap each other. With this arrangement, the heatexchange between the upper and lower layers of liquid nitrogen is donemore efficiently. Consequently, occurrence of the roll-over phenomenoncan be avoided more effectively.

The fourth example illustrated in FIG. 14 uses a bubbling device 236 inwhich a plurality of comb-like pipes 235 extend to open downward fromhorizontally arranged piping 234. This bubbling device 236 is suppliedwith an inert gas, such as nitrogen or helium, as a bubbling gas from agas source (not shown). With this arrangement, it is possible to impingebubbles produced by bubbling on bubbles generated at the bottom of thecooling jacket 18 and thereby weaken the energy of the bubbles beforethey reach the liquid surface. This prevents the liquid surface frombeing troubled. At the same time, since heat exchange is performed byproper stirring of the upper and lower layers of liquid nitrogeneffected by bubbling, liquid nitrogen in the cooling jacket 18 is hardlyrendered unstable, so the roll-over can be avoided efficiently. In thefourth example shown in FIG. 14, a safety valve means 237 is provided toprevent the internal pressure of the cooling jacket 18 from rising to apredetermined value or more. That is, although the roll-over phenomenoncan be avoided by the above arrangement of this embodiment, theroll-over yet occurs in some cases to abruptly raise the internalpressure of the cooling jacket 18 temporarily. By releasing this abruptpressure rise by the safety valve means 237, the liquid level can befurther stabilized. In addition, when an inert gas is bubbled intoliquid nitrogen as in this fourth example, bubbles produced by thisbubbling function as nuclei to make it possible to encourage nuclearboiling of liquid nitrogen. Consequently, it is possible to promoteevaporation of liquid nitrogen to use it as an efficient coldnesssource.

An operation of the plasma etching apparatus to which the treatmentapparatus control method according to this embodiment is applicable willbe briefly described below.

As in the first embodiment, a wafer W is transferred into a treatmentchamber 11 from a load lock chamber via a gate valve, and chucked andheld on the mounting surface of the susceptor 17 of a mounting table 15by an electrostatic chuck 21.

Subsequently, a cooling medium, e.g., liquid nitrogen is supplied from acooling medium supply source into the cooling jacket 18 through thecooling medium supply pipe line 211. In this case, the surface of theliquid nitrogen supplied into the cooling jacket 18 is not troubled andno roll-over is caused because of the functions of the bubble impingingplates 215 and the upper-and-lower layer heat exchanging means 216 ofthis embodiment. Consequently, evaporation and heat exchange areperformed efficiently in the liquid nitrogen, and the surface to betreated of the wafer W can be cooled to a predetermined temperature bytransfer of coldness from the liquid nitrogen. This temperature isdetected by a first temperature detecting means 35, and the controller36 operates a heater 29 or the like on the basis of the detectionsignal. Consequently, the wafer W is maintained at the predeterminedtemperature.

A treatment gas, e.g., HF is supplied into the treatment chamber 11 heldin this optimum treatment environment and at the same time RF power isapplied from an RF power supply 125 to the susceptor 17 as the lowerelectrode, thereby generating a plasma in the treatment chamber 11.Consequently, a desired etching treatment can be performed on thesurface to be treated of the wafer W. After the etching, the residualtreatment gas and the reaction products are well exhausted from thetreatment chamber 11. Thereafter, the wafer W is transferred to the loadlock chamber via the gate valve and to a cassette chamber by a transferarm. In this fashion, a series of treatment processes are completed. Inthis embodiment, as in the previous embodiments, when the etchingapparatus in which the low-temperature treatment is performed isreturned to room temperature, first and second heating means 31 and 32heat portions where occurrence of a cold leak is expected, i.e.,moisture trap portions, thereby removing moisture from these portions.Therefore, even when a treatment is performed at an ultra-lowtemperature, no cold leak takes place due to freezing and expansion ofmoisture because there is no residual moisture. This makes it possibleto effectively avoid formation of cracks in the constituting members.

(Fourth embodiment)

When a cooling medium is supplied from an external cooling medium sourceto a cooling medium container by using piping consisting of aninsulating polymer material such as Teflon in performing alow-temperature treatment, leakage of the cooling medium may take placedue to a heat shrinkage difference between the polymer material as thematerial of the piping and a metal material, such as stainless steel,used in a joint portion. The heat shrinkage difference between the twomaterials can no longer be neglected especially when anultra-low-temperature cooling medium, e.g., liquid nitrogen is used. Inaddition, when a cooling medium discharge pipe line is provided in acooling medium container independently of a cooling medium supply pipeline, a heat-insulating mechanism is also required for the coolingmedium discharge pipe line. This results in a poor space utility of thetreatment apparatus.

This embodiment provides a treatment apparatus control method capable ofimproving the throughput of a treatment by minimizing leakage ofcoldness of a cooling medium and shortening the time required forcooling an object to be treated.

That is, this embodiment provides a method of controlling a treatmentapparatus including a cooling medium supply unit which is connected to acooling medium container provided in a mounting table to contain acooling medium and supplies a cooling medium from a cooling mediumsource into the cooling medium container, a cooling medium dischargeunit which is provided on the outer circumference of the cooling mediumsupply unit and discharges a gas of the cooling medium gasified in thecooling medium container, and a reduced-pressure unit which is providedon the outer circumference of the cooling medium supply unit and isexposed to a reduced-pressure atmosphere, wherein the cooling medium isstably supplied at a high efficiency by preventing leakage of thecooling medium in a cooling medium supply path by flowing the coolingmedium through a cooling medium discharge path.

A system in which the treatment apparatus control method according tothis embodiment is applied to a plasma etching apparatus will bedescribed below with reference to the accompanying drawings. The overallarrangement of the plasma etching apparatus is similar to that shown inFIG. 1. Therefore, a cooling medium supply/discharge pipe line as thecharacteristic feature of this embodiment will be described in detailbelow.

Referring to FIG. 1, a cooling medium container, e.g., a cooling jacket18 for flowing and circulating a cooling medium, such as liquidnitrogen, is formed in a susceptor support table 16. As shown in FIG.16, this cooling jacket 18 is connected to a cooling mediumsupply/discharge pipe line 310 for supplying and discharging liquidnitrogen 301. The cooling medium supply/discharge pipe line 310 isconstituted by a cooling medium supply unit 311, a cooling mediumdischarge unit 312, and a vacuum double pipe 313. The cooling mediumsupply unit 311 supplies the liquid nitrogen 301 into the cooling jacket18. The cooling medium discharge unit 312 is formed on the outercircumference of the cooling medium supply unit 311 and dischargesnitrogen gas of the liquid nitrogen 301 evaporated in the cooling jacket18. The vacuum double pipe 313 is formed as a reduced-pressure unit onthe outer circumference of the cooling medium discharge unit 312.

The vacuum double pipe 313 has a double pipe structure constituted by anintermediate pipe 314 and an outer pipe 315. The intermediate pipe 314consists of an electrically insulating material, such as ceramics, witha low thermal conductivity and a heat stretchability smaller than thoseof metal materials, such as stainless steel. The outer pipe 315 isspaced by a predetermined distance from the outer circumference of theintermediate pipe 314 and consists of ceramics. An upper joint member317 consisting of, e.g., stainless steel is connected to the upperportions of the intermediate pipe 314 and the outer pipe 315, which areconcentrically arranged. The upper joint member 317 has a flow path 316in its central portion connected to the intermediate pipe 314 and theouter pipe 315. The upper joint portion 317 has a communication port 319which is airtightly connected to a bottom 14 via a sealing member, e.g.,an O-ring 318 and communicates with a space defined by the intermediatepipe 314 and the outer pipe 315. The upper portion of the upper jointmember 317 is airtightly connected to the bottom wall of the susceptorsupport table 16 such that an opening 320 projects above the liquidlevel of the liquid nitrogen 301. The lower portions of the intermediatepipe 314 and the outer pipe 315 are airtightly connected to a lowerjoint member 321 consisting of, e.g., stainless steel.

The cooling medium supply unit 311 includes a cooling medium supply pipe323, the lower joint member 321, and a cooling medium source 324. Thecooling medium supply pipe 323 is connected to the upper portion of aninner pipe 322, concentrically arranged inside the intermediate pipe 314and consisting of ceramics, and is so formed as to keep the airtightnesswith the upper joint member 317. The cooling medium supply pipe 323 hasan opening which is open in the liquid nitrogen 301. The lower jointmember 321 is airtightly connected to the lower portion of the innerpipe 322. The cooling medium source 324 is connected to the lower jointmember 321 and supplies the liquid nitrogen 301.

The cooling medium discharge unit 312 has an evaporator 326 connected tothe lower joint member 321 and communicating with a space formed betweenthe inner pipe 322 and the intermediate pipe 314 through a through hole325 formed in the lower joint member 321. This evaporator 326 is sodesigned as to draw nitrogen gas filled above the surface of the liquidnitrogen 301 through the opening 320 and discharge the gas outside thesystem. A protection pipe 327 connected to the bottom 14 is alsoprovided on the outer circumference of the outer pipe 315 to protect thecooling medium supply/discharge pipe line 310.

Upper and lower liquid level detectors 328 and 329 for measuring theliquid level of the liquid nitrogen 301 contained in the cooling jacket18 are arranged in the cooling jacket 18. The upper and lower liquidlevel detectors 328 and 329 transmit information about the position ofthe liquid level of a cooling medium to a controller 352. The controller352 sends information concerning the supply quantity of a cooling mediumto the cooling medium source 324 on the basis of the liquid levelinformation. The cooling medium source 324 supplies a cooling mediuminto the cooling jacket 18 through the cooling medium supply unit 311 onthe basis of the cooling medium supply quantity information. As theliquid level detectors 328 and 329, it is possible to use, e.g.,prism-like optical liquid level detectors. In this case, whether theliquid level detectors 328 and 329 are inside or outside of a liquid isdetermined by using the difference in reflectance of light, which issent to the liquid level detectors by an optical fiber means, betweenportions inside and outside the liquid.

FIG. 17 shows another example of the cooling medium supply/dischargepipe line 310 according to this embodiment. In FIG. 17, the samereference numerals as in FIG. 16 denote the same parts, and a detaileddescription thereof will be omitted.

As in FIG. 17, the vacuum double pipe 313 having a space 361 isconnected to an exhausting means, e.g., a vacuum pump 371 through a pipe370 airtightly connected to the outer pipe 315 and can thereforeevacuate the space 361. The vacuum pump 371 is controlled by thecontroller 352. The upper portion of the upper joint member 317 does notcommunicate with a treatment chamber. The space 361 is so formed as toreach the upper portion of the upper joint member 317, i.e., thevicinity of the opening 320.

With this arrangement, the space 361 of the vacuum double pipe 313 isevacuated in a direction indicated by an arrow 372 in FIG. 17 by thevacuum pump 371 and is thereby held in a predetermined reduced-pressureatmosphere. At the same time, the interior of the space 361 is isolatedfrom the varying reduced-pressure atmosphere in the treatment chamber.This reduces variations in heat loss from the cooling mediumsupply/discharge pipe line 310 resulting from variations in thereduced-pressure atmosphere in the treatment chamber. Consequently, amore stable heat-insulating effect can be obtained.

An operation of the plasma etching apparatus to which the treatmentapparatus control method according to this embodiment is applicable willbe briefly described below.

As in the first embodiment, a wafer W is transferred from a load lockchamber into a treatment chamber 11 via a gate valve, and chucked andheld on the mounting surface of a susceptor 17 of a mounting table by anelectrostatic chuck 21.

Subsequently, the controller 352 controls, in accordance with prestoredprograms, the power supply quantity of a power supply 30 for supplyingpower to a heater 29, while monitoring temperature information from afirst temperature detecting means 35, and also controls the supplyquantity of the cooling medium source 324 for supplying the liquidnitrogen 301 to the cooling jacket 18 (FIG. 16) through the coolingmedium discharge unit 312, thereby setting the temperature of the waferW at a predetermined temperature, e.g., -20° C. or less.

The controller 352 then controls an RF power supply 27 and also controlsthe flow rate of a treatment gas and the exhaust quantity of the vacuumpump to adjust the internal pressure of the treatment chamber 11,thereby generating a plasma between the susceptor 17 as the lowerelectrode and a top wall 28 as the upper electrode. Consequently, thesurface to be treated of the wafer W is etched. During the etching, thewafer W is overheated to a temperature higher than the predeterminedtemperature by the heat of the plasma. To maintain the wafer temperatureat the predetermined temperature, therefore, the controller 352 controlsthe power supply quantity of the power supply 30 and the supply quantityof the cooling medium source 324 as mentioned above.

Details of control of the cooling medium supply system for circulatingthe liquid nitrogen 301 in the cooling jacket 18 will be described belowwith reference to FIG. 16. The controller 352 sends information of apredetermined flow rate to the cooling medium source 324, and thecooling medium source 324 supplies the liquid nitrogen 301 at the flowrate based on the information into the cooling jacket 18 via the coolingmedium supply unit 311. At that time, control is so performed as to holdthe liquid level of the liquid nitrogen 301 at a predetermined positionbetween the liquid level detectors 328 and 329 while monitoring thedetection signals from the detectors 328 and 329. The liquid nitrogen301 introduced in a direction indicated by an arrow 359 in FIG. 16 intothe liquid nitrogen 301 contained in the cooling jacket 18 is subjectednuclear boiling at the bottom of the cooling jacket 18. The resultantheat exchange cools the susceptor support table 16 to transfer coldnessto the susceptor 17.

Bubbles 360 (nitrogen gas) of the liquid nitrogen 301 formed by nuclearboiling at the bottom of the cooling jacket 18 fill the space betweenthe surface of the liquid nitrogen 301 and the cooling jacket 18. Thenitrogen gas is then drawn from the opening 320 to the evaporator 326through the cooling medium discharge unit 312, heated up to theatmospheric temperature or higher, and discharged to the outside. Sincea reduced-pressure atmosphere is set in the treatment chamber by thevacuum pump, the space 361 of the vacuum double pipe 313 is evacuated ina direction indicated by an arrow 362 in FIG. 16 through thecommunication port 319 and held in a reduced-pressure atmosphere at thesame pressure as in the treatment chamber.

When the liquid nitrogen 301 is introduced into the cooling jacket 18,the interior of the space 361 of the vacuum double pipe 313 is held inthe reduced-pressure atmosphere at the same pressure as in the treatmentchamber. Therefore, no coldness leaks from the cooling mediumsupply/discharge pipe line 310, so a loss of coldness can be prevented.In addition, the low-temperature nitrogen gas produced by gasificationin the cooling jacket 18 flows into the cooling medium discharge unit312 arranged on the outer circumference of the cooling medium supplyunit 311 for supplying the liquid nitrogen 301 into the cooling jacket18. Consequently, unnecessary leakage of coldness from the coolingmedium supply unit 311 can be prevented, and this makes it possible toefficiently supply the liquid nitrogen 301 at approximately -196° C.from the cooling medium source 324. Furthermore, the cooling mediumsupply unit 311 is not in direct contact with other members, e.g., thebottom 14 and the susceptor support table 16, and the cooling mediumsupply pipe 323 having an opening which is open in the liquid nitrogen301 is connected to the portion where the upper joint member 317 is incontact with the liquid nitrogen 301. Therefore, there is no leakage ofcoldness from the cooling medium supply unit 311 through other members,and consequently the liquid nitrogen can be supplied more effectivelyfrom the cooling medium source.

As discussed above, the liquid nitrogen 301 at about -196° C. can beefficiently supplied from the cooling medium source 324 into the coolingjacket 18 without any coldness loss. Therefore, the wafer W to be etchedcan be cooled to an ultra-low temperature close to the temperature ofthe liquid nitrogen 301, e.g., -196° C. This makes it possible toimprove the throughput or the like of the etching treatment. Inaddition, since the liquid nitrogen can be supplied without any coldnessloss, it is possible to shorten the cooling time for cooling the wafer Wfrom room temperature to a predetermined temperature, e.g., -150° C.Consequently, the wafer W can be cooled to a predetermined settemperature within a short time period even if overheated by the heat ofthe plasma. This makes it possible to improve the throughput of theetching treatment and the yield of the wafer W.

In this embodiment, liquid nitrogen is used as the cooling medium, and aceramic heater is used as the heater for temperature adjustment.However, it is also possible to use, e.g., liquid helium as the coolingmedium and another type of a heater as the temperature adjusting heater.In addition, the cooling medium supply pipe airtightly connected to theupper joint member and having an opening which is open in the coolingmedium is used in this embodiment. However, a plurality of openings maybe formed in the upper joint member so that the cooling medium isradially injected into the cooling jacket.

In this embodiment, as in the previous embodiments, when the etchingapparatus in which the low-temperature treatment is performed isreturned to room temperature, first and second heating means 31 and 32heat portions where occurrence of a cold leak is expected, i.e.,moisture trap portions, thereby removing moisture from these portions.Therefore, even when a treatment is performed at an ultra-lowtemperature, no cold leak takes place due to freezing and expansion ofmoisture because there is no residual moisture. This makes it possibleto effectively avoid formation of cracks in the constituting members.

(Fifth embodiment)

In each of the above embodiments, in treating an object to be treated, aheat transfer gas, such as He gas, having a high thermal conductivity isflowed through a gap between a cooling mechanism and a susceptor toencourage heat transfer in the gap. Therefore, the object to be treatedcan be cooled relatively efficiently. On the other hand, since aheat-insulating structure between the cooling mechanism and a mountingtable is imperfect, there is a possibility that the mounting table isunnecessarily cooled in changing the set temperature of the mountingtable, as well as in the treatment. Consequently, an expensive coolingmedium, e.g., liquid nitrogen may be wasted, or a certain disadvantagemay result in maintenance. For this reason, a structure has beenconventionally proposed in which a gap is formed in a heat transfer pathbetween a susceptor and a cooling mechanism and He gas is flowed intoand out from the gap. In this structure, a heat transfer path is formedbetween the susceptor and the cooling mechanism by filling He gas in thegap. In addition, a vacuum heat-insulating layer is formed by setting aso-called vacuum state by removing He, thereby shutting off the heattransfer path between the susceptor and the cooling mechanism.

In this structure, if moisture is contained in He gas to be sealed andthis He gas is sealed in the gap present in the middle of the heattransfer path, frost forms on the surface of the gap due to cooling fromthe cooling mechanism. When the structure is returned from this state toroom temperature, the frost becomes water and gathers in a certainportion. When an ultra-low temperature is set again, the gathered waterbecomes a mass of ice to cause volume expansion, and this may lead todestruction of the structure. In this embodiment, therefore, there isprovided a treatment apparatus control method capable of preventingstructural destruction caused by a heat transfer medium, such as He gas,sealed in a gap formed in a heat transfer path.

That is, this embodiment provides a method of controlling a treatmentapparatus including a means for supplying a heat transfer medium in agap between a susceptor and a cooling jacket, wherein the dew point ofthe heat transfer medium is set to be lower than the temperature of acooling medium. In this method, it is preferable that in the heattransfer medium supply means, a means for removing moisture from theheat transfer medium be arranged in a heat transfer medium supply path.It is more preferable that a dew point meter for detecting the moisturecontent of the heat transfer medium to be supplied be also provided, andan alarm be generated or the supply of the heat transfer medium bestopped if this dew point meter detects that the moisture of the heattransfer medium reaches a predetermined amount.

This embodiment also provides a method of controlling a treatmentapparatus including a means for supplying a heat transfer medium in agap between a susceptor and a cooling jacket, a means for exhausting theheat transfer medium from the gap, a dew point meter arranged at aposition in the gap or in the vicinity of the gap and in a heat transfermedium supply path to detect the moisture content of the heat transfermedium, and an open/close valve arranged in a heat transfer mediumdischarge path, wherein when it is determined on the basis of an outputfrom the dew point meter that the detected moisture quantity reaches apredetermined amount, the open/close valve is closed to fill the gapwith the heat transfer medium. In this method, it is preferable that arelief valve for maintaining the pressure constant be provided in thepath for supplying the heat transfer medium to the gap, and the internalpressure of the gap be maintained constant when the open/close valve isclosed by a signal from a controller.

A system in which the treatment apparatus control method according tothis embodiment is applied to a plasma etching apparatus will bedescribed below with reference to the accompanying drawings. FIG. 18 isa schematic view showing the plasma etching apparatus according to thisembodiment.

This plasma etching apparatus 410 includes a treatment chamber 412consisting of, e.g., aluminum, and a treatment space 414 is airtightlyformed in the treatment chamber 412. A susceptor 416 for mounting andfixing an object to be treated, e.g., a wafer W is housed in thetreatment chamber 412. The treatment chamber 412 has a double structureconstituted by an outer cylindrical wall 412B formed integrally with atop 412A, and an inner cylindrical wall 412C having an inner flange inits upper portion. Both the outer cylindrical wall 412B and the innercylindrical wall 412C are airtightly mounted on a bottom 412D.

A gas supply pipe line 418 is provided in an upper portion of the outercylindrical wall 412B of the treatment chamber 412. The gas supply pipeline 418 can introduce a treatment gas, e.g., HF gas from a treatmentgas source (not shown) into the treatment space 414 via a mass flowcontroller or the like (not shown). A gas exhaust pipe line 420 isprovided in a lower portion of the outer cylindrical wall 412B of thetreatment chamber 412 on the side away from the side of the gas supplypipe line 418. The treatment chamber 412 can be evacuated by an exhaustmeans such as a vacuum pump (not shown) through this gas exhaust pipeline 420.

A magnetic field generator, e.g., a permanent magnet 422 for forming ahorizontal magnetic field on the surface of the wafer W is rotatablyarranged above the top 412A of the treatment chamber 412. Magnetrondischarge can be generated in the treatment chamber 412 by forming thehorizontal magnetic field by the permanent magnet 422 and an electricfield perpendicular to the horizontal magnetic field. In a space definedby the inner cylindrical wall 412C and the bottom 412D of the treatmentchamber 412 in FIG. 18, an outer circumference insulating member 424Aand a bottom insulating member 424B of an insulating frame 424 are soarranged as to cover the outer circumferential surface and the bottom ofthe susceptor 416. By arranging the susceptor 416 in the space formed bythe insulating frame 424 in this manner, the susceptor 416 is keptinsulated from the treatment chamber 412 arranged around the susceptor416.

To prevent the treatment chamber 412, the insulating frame 424, and thesusceptor 416 from contacting each other, these members are spaced apartfrom each other so that they are mutually insulated, via O-rings 426 and428 and spacers 430 and 432 made from insulating materials. In addition,a gap 434 formed between the insulating frame 424 and the susceptor 416can be evacuated by an exhaust means such as a vacuum pump (not shown)through an exhaust pipe line 436.

In this embodiment, the susceptor 416 is constituted by a three-layerstructure denoted by reference numerals 416A, 416B, and 416C. Anelectrostatic chuck 438 is mounted on the upper surface of the firstsubsusceptor 416A as the upper layer of the susceptor 416. The wafer Wis placed and fixed on the upper surface of the electrostatic chuck 438.The electrostatic chuck 438 is formed by, e.g., adhering a pair ofpolyimide resin films 438A and 438B such that a thin conductive film440, such as a copper foil, is sandwiched between them. The conductivefilm 440 is connected to a DC power supply 444 through a conductor wire442. The electrostatic chuck 438 is normally formed into a flat circularsheet in correspondence with the shape of the wafer W.

The DC power supply 444 applies a high DC voltage, e.g., 2.0 kV to theelectrostatic chuck 438 through the conductor wire 442. Consequently,static electricity is generated by polarization on the surface of theelectrostatic chuck 438, and the resulting Coulomb's force chucks thewafer W on the surface of the electrostatic chuck 438.

A heat transfer gas is supplied from a first heat transfer gas source448 to a space 446 formed between the surface of the electrostatic chuck438 and the wafer W through a valve 450 and a first heat transfer gassupply pipe line 452. In this embodiment, an inert gas, such as He gas,is used as the heat transfer gas. This heat transfer gas can transfercoldness from the heat transfer gas source 448 with a minimum loss. Theheat transfer gas is not limited to He gas but may be any given gasprovided that the gas is a heat transfer medium which does not easilyreact with a treatment gas in the treatment chamber 412 even if the gasleaks. Airtightness is not kept in the space 446, unlike in first andsecond gaps to be described later. However, since the wafer W is fixedon the first subsusceptor 416A of the susceptor 416 by the Coulomb'sforce of the electrostatic chuck 438, a heat transfer medium with apressure of less than 20 Torr can be substantially airtightly held bythis Coulomb's force.

A temperature adjusting heater 458 for adjusting the temperature of thesurface to be treated of the wafer W is provided in the secondsubsusceptor 416B as the intermediate layer of the susceptor 416. Theheater 458 is so arranged as to oppose the lower surface of the firstsubsusceptor 416A on the upper surface of the second subsusceptor 416B.A first temperature detecting means 460 for detecting the temperature ofthe heater 458 is arranged near the heater 458. The first temperaturedetecting means 460 is connected to a controller 462. In accordance withinformation of the detected temperature from the first temperaturedetecting means 460, the controller 462 drives a heater driver 464 toperform feedback control for the heater. In this embodiment, in additionto the first temperature detecting means 460, a second temperaturedetecting means 466 for monitoring is arranged near the heater 458 andthe first temperature detecting means 460. A signal from this monitoringtemperature detecting means 466 is transmitted to a temperature monitor468 which forms an interlock together with the controller 462. Thismakes it possible to prevent faulty operations of the apparatus andcontrol the heater temperature stably. In this embodiment, the firsttemperature detecting means 460 and the monitoring temperature detectingmeans 466 are arranged near the heater 458 of the second subsusceptor416B. However, these temperature detecting means can be arranged at anygiven positions where changes in the temperature characteristic of thesusceptor 416 can be detected, so they can be arranged at positionsmeeting this condition.

Furthermore, the first subsusceptor 416A is so arranged as to almostcompletely cover the outer circumferential surface of the secondsubsusceptor 416B. Therefore, it is possible to prevent externalcontamination to the second subsusceptor 416B having complicated wiringsince it is connected to an RF power supply 470, and to replace only thefirst subsusceptor 416A independently of the second subsusceptor 416B.This facilitates maintenance of the etching apparatus. In addition, aninsulating member such as an O-ring is inserted between the side wall ofthe first subsusceptor 416A and the side wall 424A of the insulatingframe 424. This prevents a treatment gas from entering this portion andthereby prevents contamination of the first and second subsusceptors416B and 416C of the susceptor 416.

A cooling jacket 474 as a cooling medium container for storing a coolingmedium 472, such as liquid nitrogen, is provided in the thirdsubsusceptor 416C as the lower layer of the susceptor 416. The coolingjacket 474 communicates with a cooling medium source 482 via a coolingmedium supply pipe line 476 and a valve 480. Liquid level detectors 484and 486 are arranged in the upper and lower portions, respectively, ofthe wall of the cooling Jacket 474. These liquid level detectors areused to monitor the liquid level of the cooling medium 472 and connectedto the temperature monitor 468. As discussed earlier, the liquid leveldetectors 484 and 486 are constituted by optical liquid level detectors.Therefore, by setting upper and lower liquid level positions, ascritical positions, in these liquid level detectors, the controller 462can control the supply of the cooling medium 472. The inner wall surfaceof the cooling jacket 474 is so formed as to be porous and can thereforecause nuclear boiling. The temperature difference between the coolingmedium 472 contained in the cooling jacket 474 and the cooling Jacket474 is kept at about 1° C. The susceptor 416 constituted by the first,second, and third subsusceptors 416A, 416B, and 416C is insulated by theinsulating frame 424 from the treatment chamber 412 which forms thetreatment space 414, thereby forming a cathode coupling with anelectrically identical polarity. The second subsusceptor 416B isconnected to the RF power supply 470 via a matching unit 488. Therefore,the susceptor 416 and the treatment chamber 412 that is groundedconstitute opposing electrodes, so it is possible to generate a plasmabetween the electrodes by applying RF power.

In the susceptor 416, a first gap 490 and a second gap 492 are formed asboundary spaces between the first subsusceptor 416A as the upper layerand the second subsusceptor 416B at the intermediate layer including theheater 458 and between the second subsusceptor 416B and the thirdsubsusceptor 416C as the lower layer, respectively. The first and secondgaps 490 and 492 are formed to connect and disconnect the heat transferpath between the susceptor 416 and the cooling jacket 474. The first andsecond gaps 490 and 492 are airtightly formed by using sealing members494 and 496, e.g., O-rings, respectively.

The first gap 490 formed between the first and second subsusceptors 416Aand 416B is connected through a pipe line 498 to a second heat transfergas supply source 504 via a valve 500 and a mass flow controller 502.Opening/closing of the valve 500 is controlled by the controller 462.When opened, the valve 500 can supply and seal an inert gas, e.g., Hegas from the second heat transfer gas supply source 504. The first gap490 is also connected to an exhausting means 508, e.g., a vacuum pumpvia a valve 506 provided in the pipe line 498. Opening/closing of thevalve 506 is controlled by the controller 462. Therefore, by opening thevalve 506 in accordance with a signal from the controller 462, thecooling medium sealed in the first gap 490 can be exhausted to evacuatethe first gap 490.

The second gap 492 formed between the second and third subsusceptors416B and 416C is connected through a pipe line 510 to a third heattransfer gas supply source 516 via a valve 512 and a mass flowcontroller 514. Opening/closing of the valve 512 is controlled by thecontroller 462. When opened in accordance with a signal from thecontroller 462, the valve 512 can supply and seal an inert gas, e.g., Hegas from the third heat transfer gas supply source 516. The second gap492 is also connected to an exhausting means 520, e.g., a vacuum pumpvia a valve 518 arranged in the pipe line 510. Opening/closing of thevalve 518 is controlled by the controller 462. By opening the valve 518in accordance with a signal from the controller 462, the heat transfergas sealed in the second gap 492 can be exhausted to evacuate the secondgap 492.

The size of the first and second gaps 490 and 492 is 1 to 100 μm,preferably about 50 μm. In this embodiment, an inert gas, such as He gasor argon gas, is sealed in the gaps 490 and 492. However, the heattransfer gas to be sealed need only be a medium which can transfercoldness from the cooling jacket 474 as a coldness source into the heattransfer path formed in the susceptor 416 with a minimum heat loss, andwhich does not react with the treatment gas in the treatment chamber 414even if the medium leaks.

The pressure of the inert gas to be sealed in the first and second gaps490 and 492 is 300 Torr or less, preferably about 70 Torr. Normally, theheat resistance of the heat transfer medium to be sealed in the firstand second gaps 490 and 492 decreases as its pressure is raised buttakes an almost fixed value when the pressure exceeds 300 Torr.Therefore, a good heat transfer path can be formed in the susceptor 416by properly selecting the pressure of the heat transfer medium withinthe above range.

In the plasma etching apparatus 410 having the above arrangement, theheat transfer path for the susceptor 416 can be connected ordisconnected by sealing or exhausting the heat transfer gas with respectto the first and second gaps 490 and 492 under the control of thecontroller 462. That is, when the heat transfer gas is sealed in thefirst and second gaps 490 and 492, the heat transfer path for thesusceptor 416 is formed. When the heat transfer gas is exhausted, on theother hand, the first and second gaps 490 and 492 are evacuated to formvacuum heat-insulating layers. Consequently, coldness from the coolingjacket 474 is no longer transferred. Consumption of the cooling mediumsuch as liquid nitrogen can be minimized when a vacuum heat-insulatedstate is set in this way. A timing at which this vacuum heat-insulatedstate is set is when loading/unloading of the wafer W is to be performedor when maintenance in which the etching apparatus itself is exposed tothe atmosphere is to be performed.

The heat transfer gas to be supplied to the first and second gaps 490and 492 is set to have a dew point lower than the temperature of thecooling medium 472 contained in the cooling jacket 474. In this case,the dew point means a moisture condensation temperature which depends onthe content of moisture in a gas. For example, a "high dew point" meansthat moisture condensation is caused at a high temperature, i.e., themoisture content is large. Therefore, the heat transfer gas ismaintained in a state in which it does not cause freezing or moisturecondensation even when cooled by the cooling medium 472. For thispurpose, a moisture removing means 522 with a structure illustrated inFIG. 19 is arranged in the heat transfer gas supply path connected to atleast one of the first and second gaps 490 and 492, which is closer tothe cooling jacket 474, i.e., the second gap 492 between the second andthird subsusceptors 416B and 416C. In the arrangement shown in FIG. 19,the moisture removing means 522 are provided not only in the transfergas supply path connected to the second gap 492 but also in the heattransfer gas supply pipe line 498 connected to the first gap 490.

More specifically, the moisture removing means 522 has a structurecapable of heating and evaporating moisture while passing a heattransfer gas through it or is constituted by a purification unit 522Ahaving a moisture absorption structure using a catalyst. In the case ofthe pipe line 510 which forms the heat transfer gas supply path for thesecond gap 492, this purification unit 522A is arranged in a bypass 524parallel to the pipe line 510. First and second open/close valves 526and 528 are arranged on both the sides of the purification unit 522A inthe bypass 524. A third open/close valve 530 is arranged in the pipeline 498 parallel to the bypass 524, at a position at which the valve530 opposes the purification unit 522A. Opening/closing of the first tothird open/close valves 526,528, and 530 is controlled by the controller462 to which they are connected. Of the three open/close valves, thefirst and second open/close valves 526 and 528 are opened when the heattransfer gas is to be supplied to the second gap 492 through the pipeline 498. The third open/close vale 530 is opened when the heat transfergas is to be exhausted from the second gap 492 through the pipe line498.

In the pipe line 510, a dew point meter 532 is arranged downstream ofthe bypass 524 in the supply direction of the heat transfer gasindicated by an arrow in FIG. 19. This dew point meter 532 is connectedto the controller 462. When the moisture content in the heat transfergas reaches a predetermined amount, the dew point meter 532 outputs asignal indicating this state. In this case, the predetermined amountcorresponds to a moisture content by which moisture condensation occursdue to cooling by the cooling medium 472. When the moisture content ofthe heat transfer gas detected by the dew point meter 532 reaches thepredetermined amount, the controller 462 generates an alarm by using,e.g., a display unit (not shown) and/or stops the supply of the heattransfer gas to the pipe line 510. In this case, of the first to thirdopen/close valves 526,528, and 530, at least the second and thirdopen/close valves 528 and 530 are closed by the signal from thecontroller 462. At that time, the valves 500 and 512 located on the heattransfer gas supply side are, of course, also closed. In this manner, ifthe moisture content reaches the predetermined amount, the supply of theheat transfer gas to the gaps is stopped. This prevents moisturecondensation in the gaps 490 and 492.

In this embodiment, a moisture concentration of 9.2×10⁻¹² (V·ppm) isobtained when the dew point of the heat transfer gas, from whichmoisture is removed by the purification unit 522A, is -150° C., so it isnecessary to select the heat transfer gas on the basis of this dewpoint. Another example of the system using this dew point meter 532 willbe described below with reference to FIG. 20.

In the example illustrated in FIG. 20, a direction switching valve 534is arranged on the downstream side in the heat transfer gas supplydirection indicated by an arrow in the bypass 524 in FIG. 19. Thisdirection switching valve 534 is normally set in a position at which theheat transfer gas can be flowed to the second gap 492. When switchedfrom this position, the valve 534 is put to a position at which the heattransfer gas is flowed toward a recovery unit (not shown).

In this embodiment, while the dew point meter 532 detects that themoisture content in the heat transfer gas is the predetermined amount orsmaller, the direction switching valve 534 is kept in the normal state.Therefore, the heat transfer gas passing through the purification unit522A can flow to the second gap 492 via the direction switching valve534. If, on the other hand, the dew point meter 532 detects that themoisture content in the heat transfer gas exceeds the predeterminedamount, the direction switching valve 534 is switched from the normalposition. Consequently, the heat transfer gas is refluxed to therecovery unit without reaching the second gap 492. Therefore, since theheat transfer gas containing moisture which causes condensation is notsupplied into the second gap 492, freezing in the gap can be prevented.

In this embodiment, the supply pressure from the heat transfer gassupply source is not disclosed. Since the second gap 492 is an airtightspace, however, it is possible to provide a relief valve for maintainingthe pressure to be supplied to the gap constant in the pipe line 510, orto provide a flow rate adjusting valve having a throttle function foradjusting the flow rate of the heat transfer gas in the pipe line 510 inaccordance with the internal pressure of the second gap 492.

This embodiment is not limited to the above arrangements but may bemodified without departing from the gist of the present invention. Forexample, as the heat transfer medium, an Ar gas, an Ne gas, an O₂ gas,an H₂ gas or the like can be used in addition to a gas such as He gas.In addition, as the means for removing moisture from the heat transfermedium, a structure as shown in FIG. 21 can be used. In FIG. 21, aportion of the pipe line 510 is dipped in a vessel 540 storing a coolingmedium, such as liquid nitrogen, liquid helium, or liquid hydrogen.Therefore, moisture in the heat transfer medium passing through the pipeline 510 is condensed as the medium passes through the cooling medium,and the heat transfer medium in this dried state is supplied to the gap.In this structure, the passage of the heat transfer medium is sometimesinterfered with by the moisture condensed in the pipe line 510. Toprevent this, as shown in FIG. 22, a portion of the vessel 540 may beextended to be dipped in a cooling medium 541, thereby extracting onlybubbles 542 generated from the heat transfer medium.

In this embodiment as described above, the dew point of the heattransfer medium is set to be lower than the temperature of the coolingmedium. For this reason, the heat transfer medium supplied to the gapdoes not cause moisture condensation even if cooled by the coolingmedium. This makes it possible to prevent freezing resulting fromcondensation of the heat transfer medium in the gap and thereby preventstructural destruction of the gap. Additionally, if moisture containedin the heat transfer medium in the heat transfer medium supply pathexceeds a predetermined amount, an alarm is generated or the supply ofthe heat transfer medium is stopped. Consequently, moisture condensationcaused by cooling from the cooling medium is avoided. The heat transfermedium is not filled into the gap unless the moisture in the heattransfer medium reaches a predetermined amount. That is, if the moistureof the heat transfer medium to be supplied to the gap is not thepredetermined amount or less, the medium is in tact discharged, and thedischarge is stopped when the moisture content reaches the predeterminedamount. Consequently, the heat transfer medium is filled in the gapafter being set in a state in which no moisture condensation is caused.The heat transfer medium filled in the gap when the moisture content isthe predetermined amount or less is kept at a predetermined pressure,i.e., filled up in the gap, thereby ensuring the heat transfer pathincluding the gap.

In this embodiment, as in the previous embodiments, when the etchingapparatus in which the low-temperature treatment is performed isreturned to room temperature, heating means heat portions whereoccurrence of a cold leak is expected, i.e., moisture trap portions,thereby removing moisture from these portions. Therefore, even when atreatment is performed at an ultra-low temperature, no cold leak takesplace due to freezing and expansion of moisture because there is noresidual moisture. This makes it possible to effectively avoid formationof cracks in the constituting members.

The first to fifth embodiments discussed above are merely examples forexplaining the treatment apparatus control method according to thepresent invention, so the method of the invention is not limited tothese embodiments. That is, the present invention can be modifiedwithout departing from the scope of the appended claims, e.g., some ofthe above embodiments can be combined.

In addition, the present invention has been described by taking thesystem using liquid nitrogen as a cooling medium. However, the effect ofthe present invention can be achieved by using a liquid helium, a liquidoxygen, a liquid hydrogen, or the like as a cooling medium.

In each of the above embodiments, the method of the present invention isapplied to a plasma etching apparatus. However, the method of thepresent invention is also applicable to a cooling mechanism of any of aCVD apparatus, an ashing apparatus, a sputter apparatus, a samplemounting table of an apparatus, such as an electron microscope, forinspecting an object to be treated at low temperatures, and a samplemounting table for evaluating semiconductor materials or devices. It isalso possible to apply the method of the present invention to an ioninjection apparatus or a burn-in apparatus for performing treatments ina reduced-pressure atmosphere. Furthermore, the arrangement of theplasma etching apparatus is not limited to those of the aboveembodiments but may be the one in which a feeder rod consisting of ahollow conductor is connected to a susceptor through a susceptor supporttable, and a plasma is generated by applying RF power of, e.g., 13.56MHz to this feeder rod.

As is apparent from the above description, according to the treatmentapparatus control method of the present invention, when the etchingapparatus is returned from a low temperature to room temperature,portions where occurrence of a cold leak is expected, i.e., moisturetrap portions are heated, thereby evaporating and removing moisture fromthese portions. Therefore, even when a treatment is performed at anultra-low temperature, no cold leak takes place due to freezing andexpansion of moisture because there is no residual moisture. This makesit possible to effectively avoid formation of cracks in the constitutingmembers. Consequently, there can be provided a stable treatmentapparatus free from failures.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and illustrated examples shown anddescribed herein. Accordingly, various modifications may be made withoutdeparting from the spirit or scope of the general inventive concept asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of controlling a treatment apparatusincluding the treatment chamber adjustable to a reduced-pressureatmosphere, a mounting table arranged in said treatment chamber to mountan object to be treated, a cooling medium container provided in saidmounting table, and a cooling medium circulating system for supplying acooling medium to said cooling medium container and discharging saidcooling medium from said cooling medium container, comprising the stepsof:treating said object to be treated while decreasing a temperature ofsaid object to be treated by cooling said mounting table by using heattransfer from said cooling medium supplied to said cooling mediumcontainer by said cooling medium circulating system; and heating, inraising the temperature within the treatment apparatus, regions in avicinity of connected portions between members constituting thetreatment apparatus to remove moisture trapped in said connectedportions.
 2. A method according to claim 1, wherein the temperature inthe vicinity of said connected portions is detected in the step ofheating regions and the heating is continued to heat said regions toreach a temperature sufficient for removing the moisture trapped in saidconnected portions.
 3. A method according to claim 2, wherein a heatingtime is controlled in heating said regions to a temperature sufficientfor removing the moisture trapped in the connected portions.
 4. A methodaccording to claim 2, wherein power supplied to a heating means iscontrolled in the heating said regions to a temperature sufficient forremoving the moisture trapped in the connected portions.
 5. A methodaccording to claim 1, wherein said treatment apparatus is one apparatusselected from the group consisting of a CVD apparatus, an ashingapparatus, a sputter apparatus, and an apparatus for inspecting anobject to be treated.
 6. A method of controlling a treatment apparatusincluding a treatment chamber adjustable to a reduced-pressureatmosphere, a mounting table arranged in said treatment chamber to mountan object to be treated, a cooling medium container provided in saidmounting table, and a cooling medium circulating system for supplying acooling medium to said cooling medium container and discharging saidcooling medium from said cooling medium container,wherein when atreatment is performed for said object to be treated while decreasing atemperature of said object to be treated by cooling said mounting tableby using heat transfer from said cooling medium supplied to said coolingmedium container by said cooling medium circulating system, a supplypressure of said cooling medium supplied to said cooling mediumcontainer is detected by a pressure detecting means provided in saidcooling medium circulating system, a pressure change rate is calculatedbased on a detected pressure value, and the supply of said coolingmedium to said cooling medium container is stopped when the detectedpressure value and the calculated pressure change rate exceed adetermined pressure value and a determined pressure change rate,respectively.
 7. A method according to claim 6, wherein when an internaltemperature of said treatment apparatus is to be raised, a vicinity of agap which traps moisture in a member constituting said treatmentapparatus is heated.
 8. A method according to claim 6, wherein thesupply pressure of said cooling medium to be supplied to said coolingmedium container is maintained constant.
 9. A method according to claim6, wherein said treatment apparatus is one apparatus selected from thegroup consisting of a CVD apparatus, an ashing apparatus, a sputterapparatus, and an apparatus for inspecting an object to be treated. 10.A method of controlling a treatment apparatus including a treatmentchamber adjustable to a reduced-pressure atmosphere, a mounting tablearranged in said treatment chamber to mount an object to be treated, acooling medium container provided in said mounting table, and a coolingmedium circulating system for supplying a cooling medium to said coolingmedium container and discharging said cooling medium from said coolingmedium container, wherein when a treatment is performed for said objectto be treated while decreasing a temperature of said object to betreated by cooling said mounting table by using heat transfer from saidcooling medium supplied to said cooling medium container by said coolingmedium circulating system, bubbles generated by boiling in said coolingmedium contained in said cooling medium container are prevented fromrising directly to a surface of said cooling medium, and regions in avicinity of connected portions between members constituting saidtreatment apparatus are heated to remove moisture trapped in saidconnected portions.
 11. A method according to claim 10, wherein heatexchange is encouraged between upper and lower layers of said coolingmedium contained in said cooling medium container.
 12. A methodaccording to claim 10, wherein said treatment apparatus is one apparatusselected from the group consisting of a CVD apparatus, an ashingapparatus, a sputter apparatus, and an apparatus for inspecting anobject to be treated.
 13. A method of controlling a treatment apparatusincluding a treatment chamber adjustable to a reduced-pressureatmosphere, a mounting table arranged in said treatment chamber to mountan object to be treated, a cooling medium container provided in saidmounting table, a cooling medium circulating system for supplying acooling medium to said cooling medium container and discharging saidcooling medium from said cooling medium container, and means forsupplying a heat transfer medium in a gap between said mounting tableand said cooling medium container, wherein when a treatment is performedfor said object to be treated while decreasing a temperature of saidobject to be treated by cooling said mounting table by using heattransfer from said cooling medium supplied to said cooling mediumcontainer by said cooling medium circulating system, a heat transfermedium having a dew point lower than a temperature of said coolingmedium is used as said heat transfer medium, a supply pressure of saidcooling medium supplied to said cooling medium container is keptdetected by a pressure detecting means provided in said cooling mediumcirculating system, a pressure change rate is calculated based on adetected pressure value and the supply of said cooling medium to saidcooling medium container is stopped when the detected pressure value andthe calculated pressure change rate exceed a determined pressure valueand a determined pressure change rate, respectively.
 14. A methodaccording to claim 13, wherein moisture is removed from said heattransfer medium.
 15. A method according to claim 13, wherein a moisturecontent in said heat transfer medium is detected, and an alarm isgenerated when the moisture content is increased to form frost on theinner surface of said gap.
 16. A method according to claim 13, wherein amoisture content of said heat transfer medium is detected, and said heattransfer medium is filled in said gap when the moisture content isincreased to form frost on the inner surface of said gap.
 17. A methodaccording to claim 16, wherein an internal pressure of said gap ismaintained constant.
 18. A method according to claim 13, wherein avicinity of a gap which traps moisture in a member constituting saidtreatment apparatus is heated, when an internal temperature of saidtreatment apparatus is to be raised.
 19. A method according to claim 13,wherein said treatment apparatus is one apparatus selected from thegroup consisting of a CVD apparatus, an ashing apparatus, a sputterapparatus, an ion implantation apparatus, a burn-in apparatus, and anapparatus for inspecting an object to be treated.
 20. A method accordingto claim 13, wherein a moisture content of said heat transfer medium isdetected, and said heat transfer medium is filled in said gap when saidmoisture content is increased to form frost on the inner surface of saidgap.